The invention relates to a method for manufacturing a cover cap for a gas bag restraint module and to a cover cap, preferably made of plastic, for a gas bag restraint module.
The tear lines on cover caps, which are usually made of plastic, are intended to permit the cover cap to tear open in a defined manner at all times over a wide temperature range.
Tear lines, or so-called initial points, from which the tearing process initiates, are formed in the cap by depressions in the plastic. Particularly at very low temperatures, it is very hard to ensure that the cap tears open within a close tolerance range of the force applied to it. Furthermore, the depressions are marked in the cover cap on the front side which is not desired. Moreover, due to the depressions, the elasticity of the region encompassed by the tear line is reduced, which is also to be avoided.
The invention provides a method that reduces the above disadvantages.
The invention provides a method for manufacturing a cover cap for a gas bag restraint module, which cover cap tears open for deployment of a gas bag. The method contains the step of treating the cap at least region-wise physically and/or chemically such that its material in a treated region has a lower strength than in an untreated state. The treated region is a predetermined tear or tear-open region for allowing the gas bag to unfold.
The method according to the invention provides for the cover cap being weakened at least region-wise by chemical and/or physical treatment in such a way that this region can tear open more easily. This is achieved by amending the material of the cap itself and its stability, i.e. not by amending the geometry of the cap through e.g. providing indentations. Depressions can thus possibly be omitted or be of lesser depth than was previously the case. Furthermore, the force needed for tearing open can be predetermined over the entire temperature range (xe2x88x9240xc2x0 C. to +80xc2x0C.) within tight limits.
The invention further comprises a cover cap made of plastic for a gas bag restraint module which cap has a predetermined tear region. The cap has a higher brittleness at said tear region than in a remainder of said cap.